1. Field of the Invention
The present invention relates to a semiconductor manufacturing apparatus and method, and more particularly to a semiconductor manufacturing apparatus and a method for upgrading uniformity of critical dimension by compensating the flare effect at wafer edge.
2. Description of the Related Art
The use of optical lithography to pattern devices that are fabricated in a semiconductor wafer (such as a silicon wafer) is well known and has been in practice for many years. Generally, a mask is used in which light penetrating elements present in the mask define a positive or a negative pattern in a photosensitive media such as photoresist. One common practice is to position light reflecting chrome on a transparent mask material, such as glass (or quartz). The light not reflected by the chrome is projected through the mask and projection optics and exposes a photosensitive material (such as a photoresist) to form a latent image therein. Depending on the positive or negative nature of the photoresist employed, one area (the exposed or the unexposed area) is developed and removed. The areas of photoresist that were removed exposes the underlying substrate areas which are then processed by various techniques, including etching and ion implantation, which in conjunction with deposition techniques form device features, such as gates, interconnects, etc. The photoresist remaining on the surface functions as a mask when the underlying layer is processed.
Uniformity of integrated circuit (IC) features"" critical dimensions or CD is necessary to achieve highest possible IC performance. One factor that affects critical dimension""s uniformity on wafers is scattered light that reach the photoresist layers of the wafers. Scattering is a well-known physical phenomena that degrades the image being formed at the target. Essentially, any light that does not propagate along the line defined by physical diffraction direction is regarded as scattered light. Scattering has also been referred to as optical noise or flare. Although scattering is undesirable, it is appreciated that some amount of scattering will always be present with the diffraction limited conventional microlithography technique. There are many causes of scattering in the lithography tool, some due to the process and others due to the tool itself. Some sources of scattering are still not well understood.
However, what is known is that the CD for a photosensitive medium may vary across its area, when formed through a microlithography process. Whether this variation in the CD is due to light scattering alone or combined with other factors, the variations are undesirable. Since the size of the resist features (such as gate or trench openings of an integrated circuit device) will depend on the combined dose produced by diffracted and scattered light in the exposed photoresist, the extent of the exposure difference on the photoresist pattern across the field of the image plane can result in feature size variations for the integrated circuit. Such variations in the feature (component and wiring) differences are undesirable, since performance of the integrated circuit may be impacted. For example, sizeable difference in the width of wiring lines can result in signal current variations.
Sizeable difference in the width of wiring line or line width is more crucial and found worse as device dimensions reduce further. Particularly, when device dimensions reduce to about 0.13 micron by using an ArF (Argon Fluoride) light source having a wave length of about 193 nanometer, flare effect or scattering of such a short-wavelength light would be a serious problem since the dose is vary small and any exposure energy difference would apparently alter tiny dimension feature and produce non-uniform circuit pattern or degrade uniformity of critical dimension. FIGS. 1-5 show how and where the flare effect affect uniformity of critical dimension on semiconductor wafers. FIG. 1 shows a diagram of line width versus exposure dose on wafers. Three stepping pitches of exposure set in a stepper are used to draw this figure. As shown in FIG. 1, smaller stepping pitch produces larger line width while a single dose is set. FIG. 2 shows how uniformity of critical dimension varies at wafer edge across a wafer. According to the phenomenon disclosed in FIG. 2, one can rationally expect that it is the flare effect, which induces the alteration of uniformity of critical dimension at wafer edge. FIG. 3 discloses how the scattered light exposes each die and increases the exposure dose on the neighboring dies of each die. The alteration of CD at wafer edge can be explained by studying FIGS. 3-5. As shown in FIG. 3, each die 102 is exposed by scattered light 104 and also receives scattered dose from scattered light 104 exposing neighboring dies except those at wafer edge. Furthermore, the source of the phenomenon disclosed in FIG. 2 can be understood further by studying FIGS. 4 and 5. In FIG. 4, a light source exposes wafer 204 on tilt pincettes 206 through lens 202. Tilt pincette 206 is disposed at wafer stage 208 and is adjustable to tilt a wafer. In FIG. 5, those dies at wafer edge which have less than four neighboring dies obviously would have alteration of CD since they receive less scattered dose from scattered light exposing neighboring dies.
In view of the drawbacks mentioned with the prior art process, there is a continued need to develop new and improved processes that overcome the disadvantages associated with prior art processes. The advantages of this invention are that it solves the problems mentioned above.
It is therefore an object of the invention to provide a semiconductor manufacturing apparatus and a method for upgrading uniformity of critical dimension by compensating the flare effect at wafer edge.
It is another object of this invention to provide a semiconductor manufacturing apparatus and a method for upgrading the yield ratio of production.
It is a further object of this invention to provide a semiconductor manufacturing apparatus and a method for compensate the flare effect of edge shot (exposure).
To achieve these objects, and in accordance with the purpose of the invention, the invention uses a semiconductor apparatus of a wafer stage for upgrading uniformity of critical dimension. The apparatus comprises means for supporting and tilting a wafer so that the wafer can be mounted on the wafer stage to be exposed in a photolithography process and means for blocking and receiving an illumination light around the circumference of the wafer mounted on the wafer stage by said means for supporting and tilting a wafer.
In another embodiment of this invention, the apparatus comprises means for blocking and receiving a illumination light around the circumference of a wafer which can be tilted and exposed along with the wafer in a photolithography process and means for mounting and tilting said means for blocking and receiving an illumination light on the wafer stage.
The invention also provides a method for upgrading uniformity of critical dimension in a photolithography process. The method comprises the following steps. First of all, a wafer on a wafer stage of a stepper is provided. Then an exposure plate circling around the wafer is provided. Finally, the wafer and the exposure plate are exposed.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention, as claimed.